British Patent No. 909,567 refers to the formation of mono(hydroxyaliphatic) ethers of dihydric phenols by reaction of 1 mol. of the dihydric phenol with 1 mol. of a suitable mono-1,2-epoxide. Thus, with glycidol, a mono(2,3-dihydroxypropyl) ether is produced, while with phenyl glycidyl ether a mono(2-hydroxy-3-phenoxypropyl) ether is obtained. Reaction of the product (1 mol.), i.e., the mono(hydroxyaliphatic) ether of the dihydric phenol, with epichlorohydrin (1 mol.) in the presence of a suitable condensation catalyst (a boron trifluoride complex) is said to lead primarily to formation of the monochlorohydrin ether, leaving the phenolic hydroxyl group largely unreacted. Thus, the reaction with, for example, phenyl glycidyl ether and a dihydric phenol HO--X--OH and subsequent treatment with epichlorohydrin is indicated to proceed as follows: ##STR2##
Such a mono(chlorohydrin ether) as that of formula V is then mixed with up to an equimolar amount of a bis(chlorohydrin ether) of a polyhydric phenol, and subjected to dehydrochlorination. The materials obtained, described as synthetic high molecular weight products of resinous character, are of a complex nature and generally solids of melting point 43.degree. C. or more. Presumably, if, e.g., phenyl glycidyl ether were used, the product obtained on dehydrochlorination would contain, amongst other compounds, a glycidyl ether of a mono-secondary alcohol formed in the following manner ##STR3##
The products are said to be useful as, or in, casting compositions.
There is no suggestion that the dihydric phenol of formula I may, under the conditions employed, react with 2 molar proportions of a mono-1,2-epoxide such as that of formula II to form the corresponding bis-adduct, of formula ##STR4## a proportion of which might, on treatment with epichlorohydrin, react to form the bis(chlorohydrin ether), which, in turn, on dehydrochlorination in the presence of the bis(chlorohydrin) ether of a polyhydric phenol, might form a corresponding diglycidyl compound.
In subsequent British Patent Specifications (Nos. 1,056,384 and 1,056,385) the same patentees reiterate that reaction of 1 mol. of a dihydric phenol with 1 mol. of a monoepoxide results in formation of a mono(hydroxyaliphatic ether of the dihydric phenol: on treatment with an excess of epichlorohydrin in the presence of sodium hydroxide or potassium hydroxide, the epichlorohydrin is said, however, to react with the phenolic hydroxyl group exclusively, leaving the aliphatic hydroxyl group unreacted. If, for example, the reaction product, (of formula III), of phenyl glycidyl ether and a bisphenol is treated with epichlorohydrin in the presence of alkali, the reaction may be represented as follows: ##STR5## i.e., the secondary alcoholic hydroxyl group remains unchanged.
In British Patent No. 1,512,814 there are described resins containing at least two photopolymerisable groups and at least two 1,2-epoxide groups, one or more of which epoxide groups are contained in 2-(glycidyloxy)propylene units. These resins are prepared by converting hydroxy groups of 2-hydroxypropylene units into glycidyl ether groups by known methods. These resins are said to be useful as coatings, particularly in the preparation of printed circuits.
We have now found that certain new diglycidyl ethers of di(hydroxyaliphatic) ethers of dihydric phenols are curable resins, many of which are of low viscosity and are particularly suitable for use in castings. The epoxide resins most commonly employed for casting have a viscosity of 10 Pa s or more at room temperature. While compositions of lower viscosity may be made by adding a non-reactive plasticiser or solvent, or by adding various monoepoxides ("reactive diluents"), this is not always desirable, because the mechanical and thermal properties of the cured resin are often deleteriously affected.